Six questions can identify HIV-positive gay men who are at elevated risk of having acute (recent) hepatitis C infection and who would benefit from further testing, according to a paper published inEurosurveillance last week. The risk score was based on data from a Dutch cohort and has been validated with separate datasets from Belgium, the Netherlands and England.

Better targeted testing of hepatitis C for gay men living with HIV could reduce the number of tests done, lowering costs and facilitating implementation in settings such as sexual health clinics. There is a lack of recommendations on how to target hepatitis C testing.

Guidelines from the European AIDS Treatment Network recommend six-monthly testing of liver function and annual testing for antibodies, for HIV-positive gay men â€śat risk for contracting acute hepatitis C infectionâ€ť â€“ but donâ€™t specify how clinicians should identify individuals who might be at risk.

A man scoring a total of 2.0 or more would be recommended to be tested for acute hepatitis C.

Of note, the risk score was developed with data from HIV-positive gay men. As the prevalence of hepatitis C is much lower in HIV-negative gay men, the risk score is unlikely to be valid for use with men who donâ€™t have HIV.

The risk score was developed from analysis of the association of acute hepatitis C with self-reported behaviour in 213 participants in the Dutch MOSAIC study. This is an observational cohort, enrolling HIV-positive gay men with acute hepatitis C (cases) and HIV-positive gay men without a history of hepatitis (controls).

It was validated with data from three other studies:

A Belgian case-control study, with data on 142 men from 2010 to 2013.

An English case-control study, with data on 190 men from 2003 to 2005.

Clinic surveys in Dutch sexual health clinics, with data on 284 men from 2007 to 2009.

In the MOSAIC cohort, the risk score had a sensitivity of 78%, in other words correctly identifying 78% of participants who had acute hepatitis C. In the three validation studies, sensitivity was 73%, 93% and 100% respectively.

In terms of specificity (correctly scoring men who did not have acute hepatitis C), in the MOSAIC cohort this was 79%. In the three validation studies, specificity was 66%, 56% and 61% respectively.

In each cohort, the risk score suggested that between 42 and 59% of the cohort should have testing for acute hepatitis C.

The area under the curve (AUC) was between 0.74 and 0.92 in each cohort.

While 2.0 was identified as the optimal cut-off for the score, the researchers provide data on the sensitivity and specificity in each cohort if different cut-off scores were used. For example, in the MOSAIC cohort, if a lower total score of 1.1 was used (rather than 2.0), the sensitivity and specificity would be 89% and 46% respectively. This indicates that fewer cases of acute hepatitis C would be missed, at a cost of providing testing to many more men who did not have hepatitis C.

If a higher score was used as the cut-off, for example 3.2, the sensitivity and specificity would be 48% and 94% respectively. This indicates that only half of those with acute hepatitis C would be recommended for testing, but that very few men who didnâ€™t have hepatitis C would need to get tested.

The researchers say that because the sensitivity of their risk score is not close to 100% it should not be relied on as the only way to identify men for hepatitis C testing, but used alongside existing practices (such as testing individuals who have abnormal liver function test results). They also say that while the specificity of the risk score is not ideal, incorrectly identifying a significant number of men as possibly having hepatitis C when they do not, these men may still benefit from behavioural interventions to reduce their risk of acquiring hepatitis C.

The risk score can successfully identify HIV-positive men who have sex with men at risk for acute hepatitis C infection, conclude the researchers. They urge its use, especially at sexual health clinics and other testing locations where men are not regularly tested for hepatitis C or where liver function is not routinely measured.